The present invention relates to a new and improved door operator for opening and closing doors on transit vehicles and the like.
In the prior art, doors on transit vehicles and the like are opened by rotating a door shaft that is connected to the door. The door shaft is rotated by an actuator that includes a piston reciprocally mounted therein, the rectilinear motion of which is translated into rotary motion to the door shaft by a helical or worm drive in the actuator. A description of such prior art device is presented in French Pat. No. 7,044,248.
A characteristic of this prior art system is that upon complete door closure, the rotating door shaft will impart a lifting movement to the doors. Lift or upward movement occurs, since further rotary motion of the door shaft is not possible and rotary motion is translated to rectilinear motion. This lifting in the door closed position is utilized to actuate locking elements that are mounted on the door frame and the door that engage each other upon door closing thereby locking and preventing further door lift. Such a door locking device is disclosed in German Pat. No. 2,805,639.
A problem exists in the prior art of lifting of the door upon engagement of the door during the closing or opening operation with an object such as a person or the like. In this particular situation, if the door engages an object, the rotary motion of the door shaft is translated into rectilinear motion causing lifting of the door. If the obstruction has been removed the door will continue to close in this lifted or non-aligned position resulting in misalignment of the door/frame in the fully closed position. It is therefore desirable to overcome this problem to ensure proper closure of the door and also to provide recycling of the door upon engagement with an object.